Bismuth phosphate carrier process for pu recovery



BISMUTH PHOSPHATE CARRIER PROCESS FOR Pu RECOVERY,

Theron G. Finzel, Cleveland, Ohio, assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. ApplicationAugust 31, 1945 SerialNo. 613,951 7 7 Claims. o1. 23:44.5

vention concerns improvements in certain phases of a separatory and concentration procedure involving the use of a bismuth phosphate carrier wherein certain improved procedure is employedin forming the carrier.

As described herein, the isotope of element 94 having a mass of 239 is referred to as 94 and is also called plutonium, symbol Pu. In addition, the isotope of element 93 having ,a; mass of- 239 is referred to as 93 Reference herein to any of the elements is to be understood. as denotingthe element generically, whether in its free state or in the form of a compound, unless indicated otherwise by the context.

Elements 93 and 94 may be obtained from uranium by various processes which do not form a part of the present invention, including irradiation of uranium with neutrons from any suitable neutron source, but preferably the neutrons used are obtained from a chain reaction of neutrons with uranium.

Naturally occurring uranium contains a major portion of U a minor ,portion of U and small amounts of other substances such as UX and UX When amass of such uranium is subjected to neutron irradiation, particularly with neutrons of resonance or thermal energies, U by capture of a neutron :becomes U which has a certain half life and by beta decay becomes nited States atent O 93 This 93 has a certain half life and by beta decay becomes 94 9. Thus, neutron irradiated uranium may contain both 93 and 94 but by storing such irradiated uranium for a suitable period of time the 93 is converted almost entirely to 94 In addition to the above-mentioned reaction, the reaction of neutrons with fissionable'nuclei such as the nucleus of U results in the production of a large number of radioactive fission products. As it may be undesirable to produce a large concentration of these fission products which must, in'view of their high radioactivity, be separated from the 94 and "further as the weight of radioactive fission products present in neutron irradiated uranium is proportional .to the amounts of 93 and 94 formed therein, it is preferable to discontinue the irradiation of the uranium by neutrons when the combined amounts of 93 and 94 reach a predetermined percentage by eight of the uranium mass, at which concentration of these substances the concentration of fission elements which must be removed is approximately the same percentage.

A number of processes have already been proposed for accomplishing the separation and concentration of Pu. One type of these processes is generically known as the bismuth phosphate type process. These processes are the inventions of others and the details of the processes 4 are described in copending applications, for example, App. Ser. No. 519,714, filed January 26, 1944, and now PatentNo. 2,785,951, granted March 19, 1957, to be referred to hereinafter, which gives details relative to the aforementioned bismuth phosphate process. Consequently, all of the details .of operation of the aforementioned processes are not described herein.

As set forth in said application Ser. No. 519,714, it has been discovered that the element Pu, under the proper conditions, can exist in aqueous solution in either of two oxidation states. In the lower of these twooxidation states, the Pu is in a form which is very efliciently carried from solution with uoride insoluble or phosphate insoluble precipitation carriers, such as the rare earth fluorides or the phosphates of bismuth, zirconium or lanthanum.

It has been found that plutonium present in a solution acidified with an acid such as nitric, sulphuricor hydrochloric and in the absence of strong oxidizing agents, or preferably in the presence of a reducing agentsuch as sulphur dioxide, can be substantially carried out of solution by co-precipitation with some insoluble. rare earth compound, such as lanthanum or cerium fluoride, or.with certain insoluble phosphates, such as the phosphates of bismuth, lanthanum and zirconium. Rare earth iodates and oxalates are also efiicient materials for substantially carrying plutonium out of solution under these conditions.' Thorium fluoride, iodateor oxalate also are efiicient carriers for plutonium under these conditions. The plutonium, when it is inthis carriable condition, is in the oxidation state of +4. The oxidation state of plutonium in this condition may be referred to as the fluoride insoluble or phosphate insoluble state.

In sharp contrast to this fluoride insoluble or phosphate insoluble state of plutonium, it has been found to an oxidation state in which it is not carried by rare earth or thorium fluoride, iodate or oxalate or by the phosphates or bismuth, zirconium or lanthanum, when these are precipitated from the solution. Under these conditions, the plutonium is oxidized to a +6 oxidation state; such plutonium in solution may be referred to as being in the fluoride soluble or phosphate soluble oxidation state. It has been found that a number of oxidizing agents are capable of oxidizing the plutonium from the fluoride insoluble or .phosphate insoluble oxidation state to the fluoride soluble. or phosphate soluble state, and the oxidizing potential required for this change amounts to about 1.0 volt on the Latimer scale of oxidation potentials. For example, it has beenv found that permanganate, periodate, dichromate and ceric ions in acid solutions can be used to'eifect this oxidation. It has also been found that reducing agents lying above the potential of about -1.0 on the Latimer scale can effect reduction from the fluoride soluble or phosphate soluble oxidation state to the fluoride insoluble or phosphate insoluble state.

That is, by having the metal 'as Pu+ aproduct precipitation or extraction may be accomplished in which a carrier precipitate brings down the Pu, leaving behind in solution a substantial portion of fission product and other sources of contamination. However, some of the activity may be carried along with the precipitate or otherwise may be occluded With the Pu. Certain contaminants such as barium, columbium, zirconium, and

lanthanum activities may be quite diflicult. to separate Patented Feb. 3,1959

dissolution, is oxidized so that Pu is obtained which remains in solution. A by-product carrier precipitate, such as a bismuth phosphate by-product precipitate, under the oxidizing conditions carries down fission products, leaving the Pu+ in solution. However, in this step some contaminants may not-separate out so that the solution remaining, which containas the Pu, may still be contaminated, although in some smaller amounts. These various cycles may be repeated several times until sufficient decontamination is accomplished. It should be kept in mind that, since the Pu is in an environment of radioactivity which may give many million of counts per minute per milligram of fission product present, the rapid, clean-cut separation of the Pu presents a considerable problem.

While prior processes have been carried out satisfactorily and give Pu recovery, in certain phases some difiiculties have been, or may, from time to time be experienced. For example, it has been noted that when the content of fission products runs high, the losses of Pu in some of the steps, such as in the by-product precipitation with a bismuth phosphate carrier, may be greater.

Without wishing to be bound by any explanation of mechanism or theory of the reasonfor this loss, it is possible that the various fission component adsorb or occlude Pu. Consequently, when the by-product precipitate is formed, which carries down the fiission products, this Pu may also be carried down either due to the aforementioned attachment or due to the fact that it is inhibited from oxidation which would place it in a soluble state. In some instances the bismuth phosphate carrier precipitated does not settle very fast and consequently the precipitation step may consume considerable time. Or the bismuth phosphate precipitate may be so finely divided that in industrial operations it may be difiicult or time consuming to dissolve all of the finely divided separated precipitate from the centrifuge bowl.

I have found that the aforementioned separatory and recovery processes illustrated by the bismuth phosphate type of process, may have included therein changes and additions for improving such processes. These improvemerits may bring about a faster settling bismuth phosphate precipitate and other better physical characteristics. That is, the precipitate may be caused to be formed in a more granular condition so that difficulties due to packing or gelatinous character are minimized, thereby facilitating washing and redissolving. In the instance of by-product precipitation, certain operations in accordance with the present invention may be carried outwhich permit better oxidation and aid in reducing Pu loss in the by-product precipitation.

The meaning of the terms product and by-product precipitate, bismuth phosphate type of process, oxidation, redissolving, direct and reverse strikes, product, and similar terms are apparent to some extent from the preceding description and will be further apparent as the description proceeds.

This invention has for one object to provide improvements in methods for the separation and recovery of plutonium.

Another object is to provide improvements in methods of forming the bismuth phosphate type of carrier precipitate.

Still another object is to provide methods for forming an improved bismuth phosphate carrier precipitate having better properties such as a faster settling rate anda structure capable of better washing and redissolving.

Another object is to provide a bismuth phosphate precipitation cycle which may be accomplished in a'shorter periodof time yet which adequately functions as respects the plutoniumrecovery.

Another object is to provide procedure for minimizing losses. of plutonium in recovery processes where either or both the'plutonium' and fission concentrations may be action takes place.

4 relatively high as compared with the contents heretofore encountered.

A still further object is to provide steps which lend themselves to combination with steps already known or practiced.

Another object is to provide a type of process which may employ materials used in existing processes, but with more efiicient action, which may be carried out in existing equipment and which is generally similar to existing practice, as respects some of theoperations.

Other objects will appear hereinafter.

In order to further illustrate a typical process which my invention may be applied to and some of the'points in such process where the invention has particular value, such an illustrative process is described below.- This illustrative process is also described for defining in further detail features such as bismuth phosphate product precipitation, bismuth phosphate by product precipitation and the like, thereby making it unnecessary in'the examples which later follow to repeat such description in detail.

Neutron irradiated uranium; is'dissolved in a suitable quantity of solvent, such as 60-70% nitric acid, giving a' uranyl nitrate solution containing plutonium. The solution'is subjected to treatment with an agent such as sodium nitrite, formic acid, H 0 oxalic acid or the like in excess for a period of about one hour at a temperature from 50 C. to 75 C. whereby any ofthe Pu which may have been oxidized to the Pu+ statein the solution step is reduced to the Pu+ state, hydrazine is eliminated or other The concentration of the solution, determined on the basis of uranyl nitrate hexahydrate, is adjusted to 20% and reagents such H and fluosilicic acid are'added.

Tothe solution is now added a source of bismuth ion to provide a concentration of' bismuth ion equivalent to 10 grams of Bi-+ ion in four liters of the uranylnitrate solution having a concentration of 20% on the basis of uranyl nitrate hexahyd'rat'e; phosphoric acid is also inc'orporated to make-the solution between .3-18'M therein, and a precipitate comprising BiPO; which carries the Pu+ comes down and is" separated fromthe" solution by filtration or centrifugation. This illustrates reduction and'an extraction or product precipitation. As will be described indetail hereinafter, the composition of bismuth reagent and the manner of formingthebis'muth phosphate carrier applicable at this point in the process are preferably in accordance with the present invention.- Consequently, thisv product precipitation step represents, in such processes, one phase where the present invention may be applied.

The MP0,, precipitate carrying the Pu, whether formed by the procedure-of the present invention or by existing practice, is dissolved in 10 'N ENC- The acidity of the solution is reduced to 6 N- HNO by dilution and the solution is made .1 M in K Cr O Sodium bismutha'te andi various other oxidizing agents may also be used. On heating the solution at 9 5- C. for 2.25 hours, the plutonium isoxidized to the Pu state. The soluti n is then diluted to 1 N acidity by addition of water, and'H 'PO is added t'o provide a suitable phosphate ion concentration for'causing the formation of a BiPO by-product precipitate. The resulting solution is heated to about C. whereupon BiPOg precipitates, carrying fission products and preferably none of the Fu The precipitate. may be removed by filtration or centrifugation' 'and discarded; This illustrates oxidation an'da byproduct precipit'ation. Likewise atthisfpo-int, iirforming a bismuth phosphate by product precipitate; the proceduresyof the present invention may be" utilized, such as the incorporation of the Bi reagent in'a'n acid mediumot' high'normality andttheincorporation of the Bi in several additions.

v In conjunction.with 'byrproduct precipitation, a proce dure termed scavenging-may sometimes: also. be carried out. However, it, is unnecessary to go into detail on this feature as the present invention is applicable in all such existing-processes whether they are exactly as described above or vary somewhat therefrom.

If repetition of the cycle is contemplated for further decontamination, the Pu in the. filtrate is reduced by introducing a rapid stream of S0 gas for five minutes and allowing the solution to stand for approximately one hour, or 'by oxalic acid, Fe+ or similar reduction and the cycle is suitably repeated.

As indicated, certain of the operations for obtaining the bismuth phosphate product and by-product precipi-- tates or other carrier precipitates are not limitations on the present invention. The product precipitation under Pu+. conditions, as indicated, may be accomplished by using any of a number of reducing agents of which sulfur dioxide, hydrogen peroxide, oxalic acid, sodium nitrite, ferrous iron, and the like are mentioned for illustration. Likewise the by-product precipitation under Pu+ conditions, as indicated, may be accomplished by a number of oxidizing agents for obtaining the Pu+ state. Dichromates, bismuthates, permanganates and the like are mentioned for illustration.

It will be further noted in forming the bismuth phosphate carriers that this may be accomplished by either adding the source of phosphate ions to a solution already containing the bismuth ions or by adding the source of bismuth ions to the liquid containing phosphate ions. In the art, it has been customary to define such procedures by the terms direct strike and reverse strike. In the direct strike bismuth phosphate is precipitated by adding the source of phosphate ions to the plutonium containing liquid which also contains bismuth ions as well as sulfuric I acid and the other components referred to above. In the reverse strike the bismuth reagent is added to the plutonium containing liquid which also contains the phosphate ions and other components. Under existing operations the so-called direct strike has been used in many instances because of the coarsely crystalline and more readily soluble bismuth phosphate carrier obtained.

Also it will be noted that the solutions containing Pu which may be treated by my invention may be the same type of solutions as heretofore treated, or may be solutions in which the concentrations of components are much higher. As apparent from the foregoing, one common type of solution containing Pu subject to separation and recovery procedures comprises a nitric acid containing liquid having a content of P11 therein. The nitric acid solution also contains other materials such as radioactive substances.

The description is now directed, in particular, to some of thefeatures of the presentinvention. As has been indicated, this invention relates to improving the efliciency of bismuth phosphate processes. As described above, bismuth phosphate carrier precipitatesmay be used both for-decontamination when the materials to be treated are under oxidation conditions and for the carrying of Pu when the materials are under reducing conditions. However, in carrying out the aforementioned steps, some losses of product and other difliculties have been encountered.

In respect to the bismuth phosphate product precipitates by a direct (H PO strike, it has been observed that theloss of Pu product in some instances may be several percent. In accordance with the present invention, it is found that such loss may be reduced to less than 1% by the following type of procedure for forming the bismuth phosphate product precipitate under reducing conditions.

It has been found that in general a direct strike followed by i a reverse, Bi(NO strike gives better recovery. Or, a reverse strike may be employed alone and'carried out by making partial additions. Thatis, a Pu containing solution is heated to 75 C. and two-thirds of the bismuth added as a Bi(NO reagent. Next, all of the phosphoric acid is added over a half hour period. This precipitates the bismuth and leaves a solution having excess phosphoric acid. The remainder, namely the last one third of the bismuth is then added. The mixture is digested for two hours at 75 C. By such procedure the loss of Pu in the supernatant liquor is only .4%.

A similar procedure may be carried out in which a greater amount, namely, nine-tenths, of the bismuth is added before the phosphoric acid addition and one-tenth is added afterward. A Pu loss of only .84% is encountered. The foregoing is generally illustrative of one aspect of the present invention.

It has also been found that the concentration of the acid of the bismuth addition as a Bi(NO reagent, namely, the normality of the HNO may be chosen so as to give abismuth phosphate precipitate of a certain crys tal size, and a bismuth phosphate precipitate which settles relatively rapidly may be obtained. That is, it has been discovered that in certain instances it may be desirable to add the bismuth reagent in nitric acid solution having a concentration within the range of 4 N to 10 N HNO rather than 2 N to obtain a bismuth phosphate precipitate that settles reasonably fast (in less than 8 minutes). Usually 5 or 6 N would be preferred as the bismuth reagents at the higher acid concentrations may tend to solidify. For example, a bismuth reagent in 7 N HNO freezes at about 21 C. Also, in general it was found that better precipitation might be obtained if there is excess phosphoric acid present in the solution when the addition of bismuth reagent is made. A system in which there is excess phosphoric acid rather than excess bismuth ions appears better for precipitation.

It has also been found, in accordance with one feature of the present invention, that small additions of fluorides EXAMPLE I The runs under this example were carried out for illustrating the effect of the acidity of the bismuth reagent in controlling the character 'of the bismuth-phosphate precipitate obtained. It Was found that the particle size of the bismuth phosphate formed was related to the acidity of the medium in which the bismuth ions were added. A faster settling precipitate which had less tendency to pack and resist washing or dissolving was formed by using Bi(NO having a high acid content.

In this example, the usual amount of bismuth, namely 2.5 g./l. was incorporated, but the nitric acid content of the medium inwhich the bismuth ions were contained varied from 2 N to 7 N. In keeping with usual procedure, the bismuth phosphate precipitation was accomplished by making the environment .8 M in phosphoric acid. Likewise, all other steps were in keeping with the phosphate precipi- Table 1 Reverse Strikes HNO; concentration of Bi+ soln 2 N Settling time of precipitate in mins From the foregoing table, it may be seen that if the' bismuth is added as a 5 N-7 N nitric acid solution instead of the lower normality nitric acid solution heretofore:

used, the bismuth phosphate carrier obtained has-a more favorable settling rate. I I

EXAMPLE II In accordance with this example, the method of forming the bismuth phosphate precipitate was varied from the usual procedures in that a portion of the bismuth was first added and then all of the phosphoric acid content was incorporated, over about a half-hour, followed by the addition of the remainder of the bismuth. In this example the normality of the nitric acid and the normality of the phosphoric acid were in keeping with usual operations. That is, the 5-7 normality described under Example I was not employed in this particular study but may be employed for still further improving the process, if desired. The precipitates were digested at 75 C. and the precipitations were carried out in 25-12 stainless steel containers.

The Pu containing solution in each run was the same type, namely, a formic acid reduced solution, reduced at a concentration of 40% on the basis of uranyl nitrate hexahydrate, andhad the same relatively high fission product content. Likewise, all the other steps for obtaining precipitate were as usual and in keeping with those described earlier herein.

The results of these several runs are summarized and compared with the control in the following table:

tically identical insettling and solubility characteristics. On this basis in general, therefore, the 5 N HNO solution is preferred.

A number of runs have been carried out utilizing bismuth phosphate carrier precipitates both in accordance with existing procedures and in accordance with the special procedures for formation of bismuth phosphate precipitates by the several additions of the present invention applied to plutonium containing solutions containing the usual content of fission activity and also fission activity several times that heretofore encountered such as content of fission activity at least twice or three times usual. It has been noted that the losses of Pu in the by-product precipitation may increase with larger fission activity. This increase may occur irrespective of whether bismuth phosphate precipitates were formed by existing practice or by the practice of the present invention. While the use of the method of formation of the bismuth phosphate of the present invention and the higher normality of the acid in the bismuth reagents improved the settling rate and character of the bismuth phosphate precipitate as described, still there may be a small loss of the Pu in a bismuth phosphate b'y-product carrier precipitates.

In accordance with the next example there are described certain supplemental additions which it has been found aided in reducing any such losses. In some in- Table 2 t I Grams, Bi+ /l. in Percent Puin' Waste Size of Runs Type of Strike Strike Reagent 2 Extraction Liquor, in nL/l. UO2(N 03):.61120 (Product) percent Precipitate 900 Direct I H3PO4 2. 5 91.4v over 8 100..- Combination: Direct' HSPO4 250 g./l. Bi 2. 5 98. 6 0.4

pg; Reverse%. 2 N HNOa 100 Combination: Direct- H3PO 250,g./l. Bi 2 5 99.7 0.84

0.9; Reverse-0.1. 2 N HNOa Inasmuch as it was noted that the tendency of bismuth nitrate to crystallize increases as the acid content increases, in this example runs were made to study the correlation between the temperature of crystallization and the nitric acid concentration. The results of this study are tabulated below:

Table 3 Temperature of Crystallization HNO Concentration Bi(l 1 );.5H2O

C. N. 9 SN. 14 7N. 21 N 27 Because of the compartively high crystallization temperature of the 7 N HNO solution (250 g. Bi/l.) it is preferable from the standpoint of greater temperature latitude on storage of the bismuth solution to use a solution 5 N in HNO rather than 7 N or to lower the bismuth content below 250 grams per liter. The latter, however, is not preferred because it might unnecessarily increase the amount of nitric acid added to the uranyl nitrate solution. It has been found as indicated above that the effects of the I-INO concentration of the bismuth solution used in the direct strike do not appear to vary much over the acidity range of 5 N to 7 N in that BiPO precipitates obtained over this range appear to be pracstances the loss may be relatively small at this point in the process and regardable as insufficient to require the addition of any supplemental reagent industrially. That is, various batches may have different specifications and other similar factors involved, hence such supplemental additions may be regarded as optional.

However, even in instances where the loss was small, it was found that the addition of supplemental reagents in accordance with the present invention generally out such losses at least 50 percent.

EXAMPLE IV In accordance with this example the Pu containing solution was treated by a bismuth phosphate by-product carrier precipitate formation, excepting that in certain of the runs a small content of sodium fluoride was incorporated. In some of the runs the content of fission products was usual and in others there was at least three times the usual quantity of fission activity. Results of these several runs under this example are shown in the following table:

The extraction precipitate referred to in the table comprised a bismuth phosphate carrier precipitate formed in a solution containing Pu. This precipitate containing Pu was dissolved in nitric acid, diluted and oxi- .dized with oxidizing agents in accordance with existing EXAMPLE v In accordance with this example a master extraction (1800 milliliters) was carried out, and the solution of the extraction precipitate, namely, the solution of a bismuth phosphate precipitate carrying Pu, (formed under reducing conditions) was divided into two equal portions. The first portion was processed through an oxidation and a by-product precipitation without the addition of any NaF while NaF was added to the second portion.

That is, NaF was added to the. extent that the oxidation was carried out in the presence of .03 N NaF. In the runs of this example the bismuth reagent was added as a 2 N HNO solution. The concentration of phosphoric acid was .8 M. The manner of addition and oxidation and all of the other details of operation were in keeping with usual practice and the same as described earlier herein.

By-product loss of Pu in the instance where no sodium fluoride was added was twice that in the instance where the fluoride was added. In this particular example the loss of Pu was .69 percent without the fluoride addition and approximately .35 percent with the fluoride addition. Since the loss was only .69, the efliciency of the process at the onset was relatively good. However, under such conditions the addition of the fluoride in accordance with this invention reduced this loss. Cross reference be obtained, but poorer Pu recovery results. However, by-the steps of the present invention both good product recovery and satisfactory character of bismuth phosphate carrier maybe obtained. In addition, and in some cases optionally when the results indicate that low Pu losses are already obtained, the by-product bismuth phosphate carrier formation may be improved by the incorporation of a small amount of sodium fluoride, hydrogen fluoride or other soluble fluoride. The present invention contemplates the utilization of all or any combination of the above features for improving bismuth phosphate precipitation.

In the above description at some points certain specific concentrations of regeants have been given for the purposes of illustration. For example, it has been indicated that .93 N NaF may be used. The choice of this particular value was based to some extent on the fission product content of the materials being processed and other related factors. Higher amounts of NaF, for example, up to :l N, may be employed. Similar remarks apply in the instance that HP is used in place of or as a supplement to NaF. In general, too large a content of these fluoride reagents would not be employed because of possible corrosion. Hence, for the definition of addition of fluorides for the purposes described herein, it may be merely indi-' cated that a small content of fluoride is employed. Similar remarks apply to the specification of some of the other reagents. For example, although it is indicated that dissolution may be accomplished in 60% to 70% nitric acid, otherlower concentrations of solvent may be employed and a longer period required for dissolution. In general the solvents'used for dissolution and related features are described in the copending applications referred to, and such steps may also be in accordance with other practice. It is to be understood that all matters contained in the above description and examples are illustrative only and is made to applicants co-pending application Serial Number 605,447, filed July 16, 1945, for Reducing Pu Losses in By-Product, wherein the aspect of fluoride addition in by-product carrier precipitation is set forth in greater detail.

From the preceding disclosure it may be seen that I have provided ways in which the formation of bismuth phosphate precipitates, both product and by-product precipitates, may be improved. One way comprises the incorporation of the source of bismuth reagent for furnishing bismuth ions in media of 4-7 N HNO acid, the 5 N acid being the preferred normality, and preferably introducing this solution into a liquid containing the required phosphate ions for precipitation. By incorporating the bismuth reagents in such media a better size bismuth phosphate particle precipitate is obtained. In accordance with another feature of the present invention, the bismuth phosphate precipitates, either product or by-product precipitates, are formed by adding from about one-half to nine-tenths of all the bismuth reagent in media of 2-7 N acid. Thereafter all of the phosphoric acid or other source of phosphate ion is incorporated. Preferably this addition is made over a period of time such as about half an hour, but longer periods up to about 2 hours may be used if desired. After the addition of all the phosphoric acid or substantially all of the source of phosphate ion, the remainder of the bismuth ion addition is accomplished. As indicated the normality of the media in which the bismuth ions are contained may be from 2-7 N, better particle size of the precipitate being obtainable by the use of the higher normality acid media. By the above procedure, better bismuth phosphate carriers may be formed and improved results obtained, exemplified by lower losses of product. If all of the bismuth is added prior to the incorporation of the phosphate ions, a hismuth phosphate carrier of satisfactory particle size may do not limit the scope of this invention, as it is intended to claim the invention as broadly as possible in view of the prior art.

I claim:

1. In a carrier precipitation process for recovering tetravalent plutonium values from an aqueous solution containing the same comprising adding sources of bismuth ions and phosphate ions to said solution to precipitate therein bismuth phosphate which thereupon carries plutonium values from solution, the improvement which comprises effecting said addition of bismuth and phosphate ions by first adding a major portion but not more than nine-tenths of the total bismuth ions to be incorporated for precipitation, then adding all of the source of phosphate ions to be incorporated for precipitation, and thereafter adding at least one minor portion of bismuth ions to effect incorporation of the remainder of the total bismuth ions for precipitation, thereby forming a bismuth phosphate carrier precipitate of improved plutoniumcarrying efficacy.

2. In a carrier precipitation process for recovering tetravalent plutonium values from an aqueous acidic solution containing the same comprising adding sources of bismuth ions and phosphate ions to said solution to precipitate therein bismuth phosphate which thereupon carries plutonium values from the solution, the improvement which comprises effecting said addition of bismuth and phosphate ions by first adding only substantially onehalf to nine-tenths of the total bismuth ions to be incorporated for precipitation, then adding all of the source of phosphate ions to be incorporated for precipitation, and thereafter adding the remainder of the bismuth ions to be incorporated for precipitation, thereby forming a bismuth phosphate carrier precipitate of improved plutonium-carrying efficacy.

3. In a carrier precipitation process for recovering tetravalent plutonium values from an aqueous nitric acid solution containing the same comprising adding sources of bismuth ions and phosphate ions to saidv solution to a I .11 precipitate therein bismuth phosphate which thereupon carries plutonium values; ,firom the solution, the improvementv which comprises effecting said addition of bismuth and phosphate ions by first adding only substantially two thirds to nine-tenths of the total bismuth ions to be incorporated for precipitation, then adding all of the phosphateions to be incorporated for precipitation, and thereafter adding, in'the form of a nitric acid solution thereof, the remainder of the bismuth ions to be incorporated for precipitation, thereby forming a bismuth phosphate carrier precipitate of improved plutonium-carrying efficacy.

4. In a carrier precipitation process for recovering tetravalent plutonium values from an aqueous acidic solu tion containing the same comprising adding sources of bismuth ions and phosphate ions to said solution to precipitate therein bismuth phosphate which thereupon carries plutonium values from the solution, the improve ment which comprises effecting said additional bismuth and phosphate ions by first adding, in the form of a hismuth nitrate solution, only substantially two-thirds of the total bismuth ions to be incorporated for precipitation, then adding, in the form of phosphoric acid, all of the phosphate ions to be incorporated for precipitation, and thereafter adding, in the form of a bismuth nitrate solution, the remainder of the bismuth ions to be incorporated for precipitation, thereby forming a bismuth phosphate carrier precipitate of improved plutonium-carrying efficacy.

5. In a carrier precipitation process for recovering tetravalent plutonium values from an aqueous acidic solution containing the same comprising adding bismuth nitrate and phosphoric acid to said solution to precipitate therein bismuth phosphate which thereupon carries plutonium values from the solution, the improvement which comprises effecting said addition of bismuth nitrate and phosphoric acid by first adding only substantially ninetenths of the total bismuth nitrate to be incorporated for precipitation, then adding all of the phosphoric acid to be incorporated for precipitation, and thereafter adding the remainder of the bismuth nitrate to be incorporated for precipitation, thereby forming a bismuth phosphate carrier precipitate of improved plutonium-carrying eflicacy.

6. In a carrier precipitation process for recovering tetravalent' plutonium values from an aqueous acidic so lutioncontaining the same comprising adding sources of bismuth ions and phosphate ions to said solution to precipitate therein bismuth phosphate which thereupon carries plutonium values from the solution, the improvement which comprises efiecting said addition of bismuth and phosphate ions by first adding only substantially onehalf to nine-tenths of the total bismuth ions to be incorporated for precipitation, then adding all of the source of phosphate ions to be incorporated for precipitation, and thereafter adding, in the form of a bismuth nitrate solution having a normality of substantially 5 to 7 in nitric acid, the remainder of the bismuth ions to be incorporated for precipitation, thereby forming a bismuth phosphate carrier precipitate of improved precipitation characteristics and plutonium-carrying efiica'cy'.

7. In a carrier precipitation process for recovering tetravalent plutonium values from an aqueous nitric acid solution containing the same comprising adding bismuth nitrate and phosphoric acid to said solution to precipitate therein bismuth phosphate which thereupon carries plutonium values from the solution, the improvement which comprises efiectingsaid addition of bismuth nitrate and phosphoric acid by first adding, in the form of an aqueous, acidic solution, only substantially one-half to ninet'enths of the total bismuth nitrate to be incorporated for precipitation, then, while digesting said plutoniumcontaining solution at approximately C., slowly adding, over a-period ranging approximately from one-half to two hours, substantially all of the phosphoric acid to be incorporatedfor precipitation, and thereafter adding, in the form of an aqueous acidic solution, the remainder of the'bismuth nitrate to-beincorporated for precipitation, thereby forming a bismuth phosphate carrier precipitate of improved plutonium-carrying efiicacy.

References Cite'din the file of this patent Seaborg et al.i Journal of the American Chemical Society, vol. 70, pp. 1128-34 (1948). 

1. IN A CARRIER PRECIPITATION PROCESS FOR RECOVERING TETRAVALENT PLUTONIUM VALUES FROM AN AQUEOUS SOLUTION CONTAINING THE SAME COMPRISING ADDING SOURCES OF BISMUTH IONS AND PHOSPHATE IONS TO SAID SOLUTION TO PRECIPITATE THEREING BISMUTH PHOSPHATE WHICH THEREUPON CARRIES PLUTONIUM VALUES FROM SOLUTION, THE IMPROVEMENT WHICH COMPRISES EFFECTING SAID ADDITION OF BISMUTH AND PHOSPHATE ION BY FIRST ADDING A MAJOR PORTION BUT NOT MORE THAN NINE-TENTHS OF THE TOTAL BISMUTH IONS TO BE INCORPORATED FOR PRECIPITATION, THEN ADDING ALL OF THE SOURCE OF PHOSPHATE IONS TO BE INCORPORATED FOR PRECIPITATION AND THEREAFTER ADDING AT LEAST ONE MINOR PORTION OF BISMUTH IONS TO EFFECT INCORPORATION OF THE REMAINDER OF THE TOTAL BISMUTH IONS FOR PRECIPITATION, THEREBY FORMING A BISMUTH PHOSPHATE CARRIER PRECIPITATE OF IMPROVED PLUTONIUMCARRYING EFFICACY. 